1. Field of the Invention
This invention relates to an improved package of carbon filament yarn, which can be smoothly unwound without generation of fluff and yarn breakage.
2. Description of the Prior Art
Nowadays, carbon filament is utilized as a basic component for combination with resins or metals to form a reinforced composite matrix. Most carbon filament is produced by heat-treating multi-filaments of acrylonitrile synthetic fiber or so-called "pitch fiber" in an oxidizing atmosphere at a temperature of 200.degree. C. to 400.degree. C. for imparting an anti-flame property, and then heating them in an inert atmosphere at a temperature of 800.degree. C. to 2800.degree. C. for carbonization. As with conventional synthetic fiber, the resultant carbon filament is often wound on a bobbin to form a yarn package of a square-end cheese type for easy handling.
A carbon filament, however, has properties quite different from conventional synthetic textile filaments, that is, the carbon filament has an extremely high Young's modulus, very low elongation, and weakness for bending as well as an extremely high surface smoothness comparing to those of the textile filaments. This means that the ability of carbon filament yarn for self-adjusting during a winding operation is poor. Therefore, it is difficult to control winding conditions for forming a package of carbon filament yarn with a winder, particularly, a winding tension of the yarn to obtain a good package of carbon filament yarn. For example, when a carbon filament yarn package is formed under a low winding tension, the yarn tends to slip over the shoulders of the package. On the other hand, a high winding tension causes breakage of component filament of the yarn during the winding operation, resulting in considerable fluff in the package.
Further, increased consumption of carbon filament has led to demands for large packaging, such as packages of 1 to 10 kg in weight. The larger the package, however, the greater the above-mentioned drawbacks. Even if a properly shaped package can be obtained, the yarn tends to slip over from the shoulders upon transport or in an unwinding process, because the package is very sensitive to mechanical shock and the yarn portions distributed therein easily move in relation to each other. With a deformed package, breakage of component filament of the yarn and fluff may occur during the unwinding operation.
In another area, the heat-treating process is a bottleneck in the production of carbon filament, because the process has to be carried out at a low temperature of 200.degree. C. to 400.degree. C. for a long period, such as from several tens of minutes to several hours. If the process is carried out at a higher temperature to reduce the processing time, serious trouble such as combustion or explosion may occur due to a run-away reaction. Under such circumstances, it is convenient to treat a plurality of carbon filament yarns in parallel in the furnace to increase productivity.
When treating a plurality of carbon filament yarns in parallel, a so-called "multi-cop winder" having a long spindle supported in a cantilever manner and a pressure roll provided along the spindle, on which spindle a plurality of bobbins are held longitudinally, may be utilized to take up the resultant carbon filament yarns. In the multi-cop winder, however, it is difficult to control the winding conditions of the packages on the spindle, whereby a difference in quality may arise between the resultant packages. In the case of large packaging, the spindle tends to bend due to the increased weight of the packages thereon, and the pressure acting between the surface of the packages and the pressure roll. Naturally, the displacement according to the bending is maximum at the free end portion of the spindle and decreases toward the root portion thereof. This causes a difference between the packages in the running yarn length between the fulcrum of yarn traversing and the surface of the package, and this causes a large difference in winding tension between the packages. In case of winding of the conventional textile yarn, the difference between the packages in the running yarn length between the fulcrum of yarn traversing and the surface of the package does not substantially cause a difference in winding tension between the packages, however, in case of winding of the carbon yarn, it causes a large difference in winding tension between the packages, since the carbon yarn has a very high Young's modulus comparing to that of the textile yarn.